1、BRITISH STANDARD BS 1715-2.3: 1989 ISO 456:1973 Analysis of soaps Part 2: Quantitative test methods Section 2.3 Methods for determination of free caustic alkali content ISO title: Surface active agents Analysis of soaps Determination of free caustic alkali UDC 661.18:620.193.423:543BS 1715-2.3:1989
2、This British Standard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board of BSIandcomes into effect on 31 July 1989 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference CIC/34
3、 Draft for comment 88/53278 DC ISBN 0 580 17284 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Policy Committee (CIC/-) to Technical Committee CIC/34, upon which the following bodies were represented: Chemical Indu
4、stries Association Consumer Policy Committee of BSI Department of the Environment Department of Trade and Industry (Laboratory of the Government Chemist) Ministry of Defence Royal Society of Chemistry Soap and Detergent Industry Association Society of Dyers and Colourists Amendments issued since pub
5、lication Amd. No. Date of issue CommentsBS1715-2.3:1989 BSI 08-1999 i Contents Page Committees responsible Inside front cover National foreword ii 0 Introduction 1 1 Scope 1 2 Field of application 1 3 Definition 1 4 Method A (Ethanol method) 1 5 Method B (Barium chloride method) 2 6 Test report 2 Pu
6、blications referred to Inside back coverBS 1715-2.3:1989 ii BSI 08-1999 National foreword This Section of BS 1715 has been prepared under the direction of the Chemicals Standards Policy Committee. It is identical with ISO456:1973 “Surface active agents Analysis of soaps Determination of free caustic
7、 alkali” published by the International Organization for Standardization (ISO). These methods supersede the method for determination of free caustic alkali given in BS1715:1963, which is deleted by amendment. Terminology and conventions. The text of the International Standard has been approved as su
8、itable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to
9、 use a full point on the baseline as the decimal marker. The symbol “ml” has been used to denote millilitre. In British Standards it is current practice to use the symbol “mL”. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Section of BS 1715”
10、. Additional information. With reference to 4.2 and 5.2, water complying with grade3 of BS3978 “Specification for water for laboratory use” is suitable, and other reagents used should be of a recognized analytical grade. With reference to 4.2.2, the potassium hydroxide ethanolic solution, expressed
11、as an amount-of-substance concentration, is c(KOH) = 0.1 mol/L. With reference to4.2.3 and 5.2.1, the hydrochloric acid standard volumetric solutions, expressed as smount-of-substance concentrations, are c(HCl) = 0.1 mol/L. Similarly, in 5.2.2 and 5.2.3, the sodium hydroxide or potassium hydroxide s
12、olutions, expressed as amount-of-substance concentrations, are c(NaOH) or c(KOH) = 1 mol/L respectively. In the definitions of T in 4.5.1 and 5.5.1 “normality” should be read as “amount-of-substance concentration (mol/L)”. In the last paragraphs of 4.5.1 and 5.5.1, “milliequivalents” should be read
13、as “millimoles”. For the purposes of 4.2.2, 4.2.3, 4.2.4, 5.2.2 and 5.2.4, the ethanol may be replaced by industrial methylated spirits complying with BS3591 “Specification for industrial methylated spirits” of appropriate strength. It should be noted that the use of industrial methylated spirits is
14、 governed by The Methylated Spirits Regulations,1983 (S.I. 1983 No.252). It is not permissible to use duty-free ethanol, received under the provisions of the Alcoholic Liquors Duties Act1972, Section10, for purposes for which industrial methylated spirits is an acceptable alternative. This Section d
15、escribes methods of test only, and should not be used or quoted as a specification defining limits of purity. Reference to this Section should indicate that the method of test used is in accordance with BS1715-2.3. A British Standard does not purport to include all the necessary provisions of a cont
16、ract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 and 2, an inside back co
17、ver and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS 1715-2.3:1989 BSI 08-1999 1 0 Introduction As soaps usually contain a small amount of unsaponified neutral fa
18、t, there is no perfect procedure for determining free caustic alkali because, when the sample of soap is dissolved, a neutral fat is more or less saponified by any free caustic alkali that is present. Both methods described in this International Standard are therefore of a conventional nature. Conve
19、ntionally, free caustic alkali is expressed as sodium hydroxide (NaOH) for sodium soaps and potassium hydroxide (KOH) for potassium soaps. 1 Scope This International Standard specifies two methods of determining free caustic alkali in commercial soaps, excluding compounded products: Method A, ethano
20、l method; Method B, barium chloride method. 2 Field of application 2.1 Method A (ethanol method) should be applied only to sodium soaps of ordinary quality, as the presence of certain additives brings in sources of error. It is not applicable to potassium soaps, because of the solubility of potassiu
21、m carbonate in ethanol. 2.2 Method B (barium chloride method) should be applied to all soft potassium soaps or mixed sodium and potassium soaps. The application of this method to sodium soaps of ordinary quality, which usually do not contain sufficient quantities of free caustic alkali to be determi
22、ned by this method, is not recommended. 3 Definition free caustic alkali in a soft soap the quantity of hydroxyl ion, reported as potassium hydroxide (KOH), which is found in solution after precipitation with barium chloride under the operating conditions described 4 Method A (Ethanol method) 4.1 Pr
23、inciple The soap is dissolved in neutralized ethanol, and the free caustic alkali is titrated with an ethanolic solution of hydrochloric acid. 4.2 Reagents The water used shall be distilled water or water of at least equivalent purity. The reagents shall have the following properties: 4.2.1 Ethanol,
24、 absolute, 20= 0,792 g/ml. 4.2.2 Potassium hydroxide, ethanolic solution, approximately 0,1N. 4.2.3 Hydrochloric acid, standard ethanolic solution, approximately 0,1 N. 4.2.4 Phenolphthalein solution, 1 g in 100 ml of 95 % (V/V) ethanol. 4.3 Apparatus Ordinary laboratory apparatus, and in particular
25、 4.3.1 Flask of approximately 500ml capacity, that can be fitted to a reflux condenser. 4.3.2 Reflux condenser 4.3.3 Analytical balance 4.4 Procedure 4.4.1 Test portion Weigh, to the nearest of 0,01 g, approximately 5g of soap. 4.4.2 Determination Pour 200ml of ethanol(4.2.1) into the flask. Connect
26、 to the reflux condenser. Bring to a gentle boil and keep at the boil for5min in order to remove carbon dioxide. Remove from the condenser and allow to cool to about 70 C. Add4 drops of phenolphthalein indicator (4.2.4). Neutralize exactly with the ethanolic solution of potassium hydroxide (4.2.2),
27、until the indicator just turns pink. Place the test portion in the flask containing the neutralized ethanol. Connect the flask to the reflux condenser and boil gently until the soap has completely dissolved. Cool to about70 C. Titrate with the ethanolic solution of hydrochloric acid(4.2.3) until the
28、 colour is just perceptibly pink, identical with that obtained when the ethanol was neutralized. 4.5 Expression of results 4.5.1 Calculation and formula The percentage of free caustic alkali in the soap, expressed as sodium hydroxide (NaOH), is where m is the mass, in grams, of the test portion; V i
29、s the volume, in millilitres, of ethanolic hydrochloric acid solution (4.2.3) used; T is the normality of the ethanolic hydrochloric acid solution (4.2.3) used. 0,040V T 100 m - BS 1715-2.3:1989 2 BSI 08-1999 The free caustic alkali content can be also expressed in milliequivalents per kilogram by m
30、eans of the following formula: 4.5.2 Reproducibility 0,02 absolute. 5 Method B (Barium chloride method) 5.1 Principle The soap and carbonate are precipitated with barium chloride and the residual alkalinity of the solution, representing the alkalinity of the free residual potassium hydroxide, is det
31、ermined. 5.2 Reagents The water used shall be distilled water or water of at least equivalent purity. The reagents shall have the following properties: 5.2.1 Hydrochloric acid, standard volumetric solution, approximately 0,1N. 5.2.2 Ethanol solution, 60 % (V/V), prepared as follows: Mix 75 ml of car
32、bon dioxide-free distilled water with125ml of carbon dioxide-free ethanol solution,95% (V/V) (which has been distilled over potassium hydroxide) and1ml of the indicator(5.2.4); neutralize to a violet colour with a0,1N solution of sodium hydroxide or potassium hydroxide, then heat under reflux for 10
33、 min. Leave to cool to room temperature and neutralize with the hydrochloric acid solution (5.2.1) until the violet colour disappears. 5.2.3 Barium chloride solution, prepared by dissolving10g of barium chloride dihydrate (BaCl 2 .2H 2 O) in90ml of carbon dioxide-free distilled water and neutralizin
34、g to a violet colour with a0,1N solution of sodium hydroxide or potassium hydroxide in the presence of the indicator(5.2.4). 5.2.4 Indicator, prepared by dissolving1g of phenolphthalein and0,5g of thymol blue in 100 ml of hot ethanol solution,95% (V/V), and filtering the solution obtained. 5.3 Appar
35、atus Ordinary laboratory apparatus and in particular 5.3.1 Conical flask of 500 ml capacity, with wide neck. 5.3.2 Reflux condenser 5.3.3 Analytical balance 5.4 Procedure 5.4.1 Test portion Weigh, to the nearest 0,01 g, approximately4g of soft soap into the flask (5.3.1). 5.4.2 Determination Add 200
36、 ml of the ethanol solution (5.2.2) and boil for10min under reflux. Add to this boiling solution15ml of the neutralized barium chloride solution (5.2.3) in small portions, mixing thoroughly. Then cool with running water to room temperature. Add 1ml of the indicator (5.2.4) and immediately titrate wi
37、th the hydrochloric acid solution (5.2.1) until the colour turns green. 5.5 Expression of results 5.5.1 Calculation and formula The percentage of free caustic alkali in the soft soap, expressed as potassium hydroxide (KOH), is where The free caustic alkali content can be also expressed in milliequiv
38、alents per kilogram by means of the following formula: 5.5.2 Reproducibility 0,05 absolute. 6 Test report The test report shall include the following particulars: a) the reference of the method used; b) the results and the method of expression used; c) any unusual features noted during the determina
39、tion; d) any operation not included in this International Standard, or regarded as optional. VT m - m is the mass, in grams, of the test portion; V is the volume, in millilitres, of hydrochloric acid solution (5.2.1) used; T is the normality of the hydrochloric acid solution (5.2.1) used. 0,056V T 1
40、00 m - VT m -BS1715-2.3:1989 BSI 08-1999 Publications referred to See national foreword.BS 1715-2.3: 1989 ISO 456:1973 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on s
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